I definitely don't *need* ExpertFlyer by any stretch... I usually fly around once per month, meaning that paying $9.99/month for a service designed for road warriors probably counts as a dumb purchase. I tend to look at it like a fun toy, since I get my jollies by searching for availability on random routes just for the heck of it. What if we wanted to go to Siem Reap in September? How would we get there? What miles would I need? Sure, I could find all this out by going through various mileage programs, but it's easier to have all the data right there in ExpertFlyer. That said, I've gotten a ton of value out of the flight alerts that you can set up - maybe not $120/year, but certainly enough to get me hooked on having the service. In the few months I've been a member, I have been notified about first class availability for Justine's return flight from New Zealand, business class availability on Swiss during my trip to Europe next year, and today maybe the biggest thing of them all - a non-bulkhead window seat on Delta! The one time I've sat in the first class bulkhead on a Delta A320, I was unpleasantly surprised by the fact that the bulkhead wall is about an inch and a half from your face, giving you less room for your feet than you'd have in economy. I just recently flew United's updated A320 first class product and was happy to see the generous amount of legroom they give the bulkhead seats, which really puts Delta's product to shame. So when I booked this flight, I decided to spring for first class given the small premium over economy, but the only available seat was 1D. I'd still rather have a wider seat with less legroom, so I took it and set a seat alert for any other window seat. Cut to just now, when ExpertFlyer emailed to tell me that 2A was now available - thirty seconds later I was in my Delta account confirming my seat change to 2A. Score!
Again, this is a pretty small deal and doesn't on its own justify ExpertFlyer's fee (especially because you can create some seat alerts for free). Still, it's a fairly small price every month and it has demonstrably improved my experience when I do fly, so I'd definitely say it's worth it, in case you were on the fence.